Bleaching operations using hydrogen peroxide or compounds capable of yielding hydrogen peroxide, hereinafter referred to as peroxygen bleaches, have been extensively described in the art. Such peroxygen bleaches have an advantage over chlorine bleaches, in that they are milder bleaches. This advantage is especially significant in the context of a fabric laundering operation because peroxygen bleaches are safer to fabric colors and are non-yellowing to white fabrics.
A major drawback of peroxygen bleaches is that they are less active than chlorine bleaches at low temperatures which are often encountered in modern laundering operations, or in the treatment of hard surfaces. Thus, peroxygen bleach activators have been developed, which have been extensively addressed in the art. These activators can be transition metal or peracid precursors. Peracid precursors react with hydrogen peroxide to yield peracids. Peracids are the "activated" bleaching species which are efficient at low temperatures.
Such peracid-yielding systems are also of interest in non-laundry applications, as they provide disinfectancy benefits in addition to some bleaching benefits, due to the peracid. Such benefits are particularly desirable on kitchen and bathroom surfaces, especially in toilet bowls.
Peroxygen type bleaches are also advantageous over chlorine bleaches in terms of environmental compatibility, and there is a continuous need for the development of products which are ever more environmentally compatible. Specifically, there is a need to develop environmentally compatible peracid precursors.
In addition, products comprising both a peroxygen bleach and an activator need to meet a balance between shelf-stability of that combination, and its capability to react as fast as possible in water, during the bleaching operation. These two characteristics are somewhat contradictory. This problem is especially acute in liquid aqueous compositions, but it also exists in dry products where shelf stability can become an issue if the product is subjected to humid environments, as the product can become damp and may lose some activity.
EP 241 137 proposes to use solid peracid precursors which are insoluble in an acidic aqueous medium, but become soluble in an alkaline medium. Such a system is said to be stable upon storage, but all activators proposed therein comprise benzene rings and are therefore not particularly environmentally compatible.
EP 210 674 proposes P-sulphophenyl carbonates as hydrogen peroxide activators. All these compounds comprise phenyl groups, thus are not environmentally compatible.
EP 396 287 teaches pH control in a bleaching process using hydrogen peroxide and a peracid precursor, wherein the wash pH is initially raised, then lowered to promote bleach efficiency. That document contains an exhaustive list of the peracid precursors described in the art.
It has now been found that the acylated citrate esters according to the present invention would meet all the objects described hereinabove. The acylated titrate esters according to the present invention are fully environmentally compatible as they eventually degrade into citric acid and alcohols. They are particularly stable upon storage in a mildly acidic medium, compared to the activators of the art, even in a liquid composition comprising a peroxygen bleach.
Some of the acylated citrate esters according to the present invention also provide an additional benefit in that they exhibit interesting building capacity. Such benefit is particularly useful in the context of a laundering application.
The acylated citrate esters according to the present invention thus allow great flexibility in that they can be used in any product, granular or liquid, with or without a peroxygen bleach.